This invention relates to a method and apparatus for subjecting digital data to a compression coding/decoding process, and more particularly to a digital data processing system effective for transmitting or recording, or receiving or reproducing wideband digital data while maintaining the compatibility with a format dealing with narrow-band digital data by utilizing the digital data compression coding/decoding method.
More specifically, a digital data processing system according to this invention relates to a lossless compression coding method and apparatus for digital data, a decoding method and apparatus for digital data subjected to the lossless compression coding process, a transmission (recording) method and transmission (recording) apparatus for digital data subjected to the lossless compression coding process, a reception (reproducing) method and reception (reproducing) apparatus for digital data subjected to the lossless compression coding process, and a recording medium on which digital data subjected to the lossless compression coding process is recorded.
As is well known in the art, the technique for converting an audio signal into a digital form and recording and reproducing the same with respect to a recording medium is widely accepted since CDs (compact disks) were put on the market. The technique received much attention in those days as means for providing the high quality of sound (high fidelity) which could not be attained at all by using an analog record and the idea that the high fidelity can be attained by use of CDs has been fixedly accepted.
However, ten years have passed since such CDs were first put on the market and various audio devices have been developed, and now, it is widely recognized that the sound quality of such CDs is not sufficiently high as the presently available high fidelity.
Recently, a DVD (Digital Video Disk) which is a disk having the same diameter as the CD and can record digital video data and digital audio data is developed and the standardization thereof is positively considered. In the DVD, in order to record long-time digital video data and digital audio data, the digital video data and digital audio data are first subjected to the compression coding process and then recorded on the disk with high density.
In the DVD, a special attention is paid to attain the sound quality improved over that of the CD. More specifically, it is possible to record non-compressed digital audio data as well as digital audio data which is subjected to the compression coding process.
As the non-compressed digital audio data, data items ranging from data in the format in which the sampling frequency is 48 kHz and the bit width of one sample is 16 bits as in the case of CD to data in the format in which the sampling frequency is 96 kHz and the bit width of one sample is 24 bits at maximum can be dealt with. This means that the reproduction band can be increased from 20 kHz to 48 kHz and is thus widened more than two times in comparison with a case of CD and the dynamic range can be significantly improved from 98 dB to 136 dB.
However, digital audio data recorded on the present DVD is dealt with only as data attached to digital video data. Therefore, it is strongly required to develop disks exclusively used for audio data of ultra-high fidelity for dealing with digital audio data as main data and enhancing the sound quality to maximum. The concrete requirement for ultra-high sound quality is to widen the audio band to approx. 100 kHz by taking into consideration the frequency bands of various musical instruments and the frequency bands which recording devices can deal with.
In a case where disks exclusively used for audio data of ultra-high fidelity are newly developed, the compatibility with DVDs which are already standardized becomes a problem. That is, the so-called forward compatibility that a player for reproducing disks exclusively used for audio data which are newly standardized can reproduce digital audio data recorded on a previous DVD and the backward compatibility that a player for reproducing the previous DVD can reproduce disks exclusively used for audio data which are newly standardized are required.
The DVD player reproduces disks exclusively used for audio data within a range of the performance previously standardized in the function and sound quality. More specifically, even when digital audio data of 100 kHz is recorded, the DVD player can reproduce components of up to 48 kHz bandwidth.
For the forward compatibility, it is more preferable if the disk formats of the disk exclusively used for audio data and the DVD are common, but basically, it is possible to design the player for disks exclusively used for audio data so as to cope with reproduction for both of the above disk formats.
For the backward compatibility, the DVD player of the previous standard cannot recognize the newly standardized format, and therefore, it is necessary to carefully design the newly standardized format of disks exclusively used for audio data.
Further, since a required bit capacitance and the bit rate used increase in non-compressed digital audio data in which the band is wide and the bit width of one sample is large, it is difficult to record long-term data even when data is recorded on the disk with extremely high density.
Specifically speaking, the bit rate of 24-bit digital data in which the sampling frequency is 192 kHz and the bit width of one sample is 24 bits corresponds to six times the bit rate of 16-bit digital data in which the sampling frequency is 48 kHz and the bit width of one sample is 16 bits as in the case of CD.
For this reason, it becomes necessary to save the number of data bits in order to record long-term digital audio data on the disk, and as a result, it becomes necessary to subject the digital audio data to a compression coding process.
As compression coding processing means, a compression coding process which causes a deterioration in the sound quality in principle is not used, but a so-called lossless compression coding (lossless coding) process capable of completely reproducing data prior to the compression coding at the time of decoding without causing any deterioration in information in the course of compression coding is required for the purpose of attaining ultra-high fidelity.